But do you really think that, back then, he would have made the relationship "I've been turned into a devil person as a consequence of me being an ass?"

His original statement was a sentence ending in a period, but you are asking a question about it, so the question mark is appropriate because you are the current speaker.

Guessed so. But it ends up being the same if I made a statement and Seymour made a question, right? I guess that's not too much of a problem in practice but the ambiguous grammar confused me._________________Welcome to Sinfest, the only place with a 46 pages long thread about sentient toasters